Fibrous material



Feb. 27, 1962 w. T. LARMAN ETAL 3,023,075

FIBROUS MATERIAL Filed. Nov. 14, 1957 3,023,075 FBRQUS MATEREAL William Thomas Larman, fielwyn George Hawtin, and John Downing, all of Spondon, near Derby, England, assignors to British Ceianese Limited, a corporation of Great Britain Filed Nov. 14, 1957, Ser. No. 696,562 Claims priority, application Great Britain Oct. 26, 19:54 16 Claims. (Cl. 118-5 3) This application is a continuation-in-part of our copending application Ser. No. 537,998, filed October 3, 1955, and now abandoned, the entire disclosure of which is hereby incorporated by reference.

The invention relates to the manufacture of novel fibrous material which may be used in the production of filter tips for cigarettes.

According to the invention we make novel fibrous rodlike material of low density, suitable for use in the production of cigarette filter tips, by extruding a solution of a filament-forming substance, advantageously a thermoplastic filament-forming substance and in particular cellulose acetate, into a coagulating liquid through a large number of closely spaced orifices distributed over substantially the whole of a circular area, and drawing the filaments so formed through and out of the coagulating liquid at a linear speed (take-up speed) less than half the linear speed at which the solution is extruded (extrusion speed). The ratio of the take-up speed to the extrusion speed is preferably below 1:4 and especially below 1:5 or 1:8, and it may be as low as 1:15 or 1:50.

The invention relates to a method of making fibrous rod-like materials. This material is characterised not only by being rod-like in form, but also by being made up of a large number of continuous filaments of the cellulose acetate or other filament-forming substance, which are highly curled and are so entangled with each other as to form a unitary structure having large air spaces.

The coagulating liquid employed in the manufacture of the new material is preferably one which causes rapid precipitation of the filament-forming substance from the spinning solution, in contrast to the usual practice in wet spinning, in which the coagulating liquid is chosen with a view to effecting the precipitation relatively slowly. For example, when the spinning solution is an acetone solution of cellulose acetate, a very good product is ob tained using water as the coagulating liquid; towns water and river water as usually satisfactory, but if desired there may be used water which is substantially free from metal cations, such as distilled water or water from which the metal cations have been removed by an ionexchange process, usually termed demineralised water. The water will of course in practice contain a proportion of acetone derived from the spinning solution, and it is desirable that the proportion of acetone in the water should not exceed 20%, and is preferably less than by weight. Indeed, whatever spinning solvent or coagulating liquid is used, the amount of solvent in the coagulating liquid is best kept below 20% and especially below 10%.

The spinning jet employed to form the filaments preferably contains more than 200 orifices, and better more than 400; for example it may contain 4002500 orifices. They should be spaced apart by less than 2 mm., and preferably about 0.25-1.5 mm., between centres, and most advantageously have a diameter between about aszasrs Patented Feb. 27, 1962 0.025 and 0.125 mm. The spacing must not of course be so close that the extruded filaments coalesce and should always exceed the orifice diameter. While the orifices will usually be of circular cross-section for the sake of convenience and ease of formation, orifices of non-circular cross-section, e.g. of an elliptical, rectangular or slot-like cross-section, or a cross-section having reentrant angles, may be used. The orifices need not all be identical.

While the invention is not restricted to the use of any particular design of wet spinning apparatus, except so far as may be necessary to fulfill the conditions set out above, good results are obtained by using a device of the kind in which the filaments are drawn up through a fairly narrow tube through which, and preferably up which, the coagulating liquid flows. Apparatus of this kind will be found described for example in United States applications Ser. No. 323,788 of P. F. C. Sowter and F. B. Hill, filed December 3, 1952, and now abandoned, and Ser. No. 451,191 of R. I. Brown and J. Downing, filed December 20, 1954, and now abandoned (and the corresponding British Patents Nos. 720,187 and 787,557) and United States Patent No. 2,732,586 of W. H. Bradshaw and R. O. Denyes.

After leaving the coagulating bath the fibrous material may be at once wound up or otherwise collected, e.g. in a sliver can, or it may be given a modifying treatment. In any event, before it is used in the production of filter tips it is preferably subjected to compression so as to increase the tightness of packing of the individual filaments, and so decrease the size of the air spaces between them. It is also advantageous to give the surface of the material a treatment whereby it is rendered smoother, e.g. with the aid of heat (when the filament-forming substance, is thermoplastic), or a solvent for the filamentforming substance, or both. This treatment to modify the surface may be applied before, simultaneously with or after the material is compressed, or more than one such treatment may be given at different times.

One very usefulmethod of compressing the material consists in rolling it between two surfaces. Preferably ese surfaces are parallel and are spaced apart by a distance equal to the diameter desired for the final product, but they may be at a small angle such that the material as it moves between them can be gradually compressed until it has the desired diameter. When, as is preferred, the material is made of cellulose acetate or another thermoplastic filament-forming substance, one or both of the said surfaces may with advantage be kept at a temperature sufficient to soften the thermoplastic substance on the surface of the material to some extent, so increasing the smoothness and homogeneity of the outer layer of the material without substantially affecting the filaments in the body of the material otherwise than by compres sion alone. Thus, for example, when an acetone-soluble cellulose acetate material is being made, one or both of the surfaces between which it is rolled may be at a temperature of about C. or 200 to 230 or 240 C., the optimum value depending inter alia on the duration of the treatment and the amount by which the material is compressed in the course of the treatment.

Before being subjected to the rolling operation, the ma terial may if desired be cut into fairly short lengths, e.g. into lengths between 2 and 24 inches. Thus the material after it has left the coagulating liquid, and conveniently while it is still wet, may be passed into a device wherein it is cut up into pieces of the desired length, which are then immediately forwarded to arolling device. n the other hand, the individual pieces may be stored before being rolled, or the material can be subjected to the rolling operation continuously with its production, or otherwise without being cut up.

Various methods and forms of apparatus may be employed for carrying out the rolling operation, according to whether the material is in the form of short lengths or a single continuous length. For example short lengths of the material may be rolled between a fixed concave surface of part-cylindrical form and a coaxially mounted roller of suitably smaller diameter, which is preferably mounted above the concave surface, the fixed surface or the roller or both being heated if required. Again, short lengths of the material may be rolled between two parallel plates one of which reciprocates relatively to the other, and one or both of which may be heated, the arrangement being such that the material is either rolled in one direction only, or is rolled in both directions and ejected from the device at the same end as it entered it. In another method a continuous length of the material may be fed between two suitably spaced flexible metal bands travelling longitudinally at the same speed and arranged so that one at least can be reciprocated laterally, for instance by a mechanism such as is described in US. Patent No. 2,226,137; either or both the bands can be heated.

A superficial heat treatment during the rolling operation may be replaced or supplemented by the application of a solvent or strong swelling agent to the surface of the material. Thus instead of being heated to a temperature high enough to soften the material superficially, the rolling surfaces (or one of them) may be wet with a suitable liquid, preferably a solvent which is sufficiently volatile to make easy its subsequent complete removal by evaporation; for example when a material made of filaments of an acetone-soluble cellulose acetate is being treated, the surfaces may be wet with acetone. Higher boiling liquids however can be used provided they are readily completely removed either by evaporation at a temperature at which the material will not be damaged, or by washing for example with water. If desired a liquid which is a solvent or strong swelling agent for the filament-form-ing substance only at elevated temperatures may be employed in conjunction with a rolling surface or surfaces heated to such a temperature.

Another method of compressing the material consists in passing it through one or more smooth dies, which are preferably rotated and which may be heated to a temperature such that they slightly soften the surface of the material in contact with them. Since the rod-like material as initially formed is neither very stiff nor very strong, it is necessary that it should not meet with much resistance in passing through such a die. To this end the entrance to the die may be flared, and the material may initially be wet with some liquid that will reduce the friction between the material and the die, e.g. water or an aqueous emulsion of an animal or vegetable oil. Rotation of the die has the effect not only of facilitating passage of the material through it, but also of exerting a smoothing action on the surface of the material.

A final product having a particularly smooth surface can be obtained by subjecting the material, after it is compressed, to the combined action of friction and a solvent. Thus a cellulose acetate material may be drawn through an annular wick or the like kept wet with acetone and adapted to bear on the material passing through it, the acetone being removed from the material by evaporation or washing before it can penetrate it to any considerable depth.

The invention is illustrated in the accompanying drawing in which:

FIGURE 1 is a side view in section of an apparatus which may be used to compress the rod-like material;

FIGURE 2 is a schematic illustration of an apparatus for producing the rod-like product commencing with a dope of filament-forming material;

FIGURE 3 is a view partially in section, of the shaping and cutting operation; and

FIGURE 4 is a perspective view of a cigarette, with a portion of the wrapping broken away, including as a filter the rod-like product produced by the apparatus of FlGURE 1.

Referring now to the drawing, the apparatus consists essentially of an upwardly facing concave base member 1, of which the upper part forms a fixed concave rolling surface 2 of part-cylindrical form, and the lower part 3 forms with the upper part 2 a hollow space provided with an inlet 4 and outlet 5 for a heating fluid. A roller 6 is mounted on a rotatable shaft 7 which is coaxial with the rolling surface 2, and adapted to be rotated by any suitable driving means (not shown). An inclined plane 8 having its surface continuous with one end of the rolling surface 2 serves to feed short lengths 9 of the material to be treated into the space between the fixed rolling surface 2 and the surface of the roller 6, and a chute 19 at the other end of the rolling surface 2 leads material leaving the device to a container 11.

In operation, a heating fluid at the desired temperature is passed through the interior of the concave base member 1, and the roller 6 is rotated in an anticlockwise direction (as viewed in the figure). Short lengths 9 of the material to be treated are fed at regular intervals to the inclined plane 8, down which they pass into the space between the fixed rolling surface 2 and the surface of the roller 6. As the roller rotates these lengths of material are simultaneously compressed somewhat and caused to travel with a rolling motion until they reach the chute 10, down which they pass into the container 11.

This device can be modified in various ways. For example, instead of th inclined plane 8 there may be employed a positive feeding arrangement consisting for example of parallel conveyor bands, or a single wide conveyor band, and a similar device may be employed instead of the chute 10. Furthermore instead of discharging directly to a container, the treated material may be passed either to a conveyor belt or the like, by means of which it is transported to another machine, e.g. a cutter adapted to cut it up into the shorter lengths appropriate for filter tips, or to storage, or it may pass directly to a cutter. The base member 1 ma, if-desired, be heated otherwise than by means of a heating fluid, e.g. electrically, and the roller 6 may be heated as well as or instead of the base member 1.

The short lengths of the material treated in the apparatus of FIGURE 1 can be produced as shown in FIGS. 2 and 3. In FIG. 2 a dope or solution of filamentforming material is supplied to a spinnerette 12 positioned in a spinning column 13 filled with a coagulant vI i. Fresh coagulant is supplied at 15 and spent coagulant overflows at the top of column 13 into a headbox 16 from which it drains at 17. Filaments 18 form in the coagulant 1dand pass upwardly and then about an idler roll 19, being pulled along by driven rolls 20 operating at a slower peripheral velocity than the linear rate at which the dope leave spinnerette 12.

The filaments in the form of a cylindrical material 21 (FIGURE 3) pass through an annular sparger 22 which wets the material with a lubricant. The material passes through a tapered shaping die 23 which forms it into the desired cross-section. A reciprocating blade 24 cuts the material into predetermined lengths 9 which are then processed as described in connection with FIGURE 1.

The processed lengths 9, after being further out to desired length if necessary, are then wrapped together with tobacco 25 (FIGURE 4) in paper 26 to produce a filter cigarette 27.

The invention is further illustrated by the following A efeemerri In Example I A 26% solution of cellulose acetate in acetone is extruded into water at C. through a spinning jet containing 500 orifices, each 0.06 mm. in diameter, arranged uniformly over the area of a circle of diameter 24 mm, with a spacing between centres of about 0.9 mm. The extrusion speed is about 100 metres per minute and the take-up speed about metres per minute. An approximately cylindrical material having a mean diameter of about 6.0 mm. is obtained. This is then rendered denser and superficially smoother by rolling it in an apparatus such as that described above by reference to the drawing, the spacing between the surface 2 and the roller 6 being 5 mm., and the base member 1 being held at a temperature of 210 C.

Example 11 A 26% solution of cellulose acetate in acetone containing 5% by weight of water is extruded into water at about 18 C. through a spinning jet containing 1261 orifices each 0.05 mm. in diameter arranged uniformly over the area of a circle of diameter 20 mm., with a spacing between centres of about 0.5 mm. The extrusion speed is about 100 metres per minute and the take-up speed about 3 metres per minute. An approximately cylindrical material of diameter about 7.2 mm. is obtained, which is rendered denser and superficially smoother by rolling it as described in Example 1, except that the spacing between the surface 2 and the roll r 6 is 6 mm., or by passing it through a rotating metal die of diameter 6 mm. heated to 200 C.

The materials produced in accordance with both these examples, when cut up into short pieces of appropriate length, is found to provide very satisfactory filter tips.

While the invention has been described with particular reference to cellulose acetate materials, it can be applied to materials of other filament-forming substances, for instance cellulose esters of other fatty acids containing up to four carbon atoms in the molecule, or regenerated cellulose. When cellulose acetate is used it need not be acetone-soluble; thus a solution of a cellulose triacetate (i.e. a cellulose acetate of acetyl value above about 59% and especially above 60% calculated as acetic acid) in acetic acid may be extruded into water, or a solution in methylene chloride or a mixture of methylene chloride with a small proportion of methanol or ethanol may be extruded into a bath of one of these alcohols.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process which comprises extruding a solution of a filament-forming substance into a coagulating liquid through at least 200 orifices distributed over substantially the whole of a circular area and spaced apart by less than 2 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is less than half the extrusion speed and compressing said mass into a cylindrical structure of predetermined cross-section.

2. Process which comprises extruding a solution of a filament-forming substance into a coagulating liquid through at least 200 orifices distributed over substantially the whole of a circular area and spaced apart by less than 2 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is less than /s of the extrusion speed, and subsequently forming said material into cigarette filter tips.

3. Process which comprises extruding a solution of a filament-forming substance into a coagulating liquid through a least 200 orifices distributed over substantially the whole of a circular area and spaced apart by less than 2 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between A1 and of the extrusion speed and compressing said mass into a cylindrical structure of predetermined cross-section.

4. Process according to claim 3 wherein said solution is extruded vertically upwards.

5. Process which comprises extruding a solution of a cellulose acetate into a coagulating liquid through at least 200 orifices distributed over substantially the whole of a circular area and spaced apart by 0.25-l.5 mm. between centres drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between A3 and of the extrusion speed, and subsequently forming said material into cigarette filter tips.

6. Process according to claim 5, which comprises extruding the solution through more than 400 orifices of diameter between 0.025 and 0.125 mm.

7. Process according to claim 6, which comprises extruding the solution into a coagulating liquid consisting of a non-solvent for the cellulose acetate in which the concentration of solvent is kept below 20% by weight.

8. Process which comprises extruding an acetone solution of an acetone-soluble cellulose acetate into a coagulating liquid consisting of water in which the concentraion of acetone is kept below 10% by weight through at least 400 orifices of diameter between 0.025 and 0.125 mm. distributed over substantially the whole of a circular area and spaced apart by 0.25l.5 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between A2 and of the extrusion speed, and subsequently forming said material into cigarette filter tips.

9. Process according to claim 8 wherein said solution is extruded vertically upwards.

10. Process according to claim 1, which comprises the step of compressing the rod-like material, while maintaining its substantially cylindrical form, after it has left the coagulating liquid.

11. Process according to claim 10, which comprises the step of compressing the rod-like material by rolling it between two surfaces spaced apart by a distance less than the initial diameter of the rod-like material.

12. Process which comprises extruding a solution of a thermoplastic filament-forming substance into a coagulating liquid through at least 400 orifices distributed over substantially the whole of a circular area and spaced apart by 0.251.5 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between Ma and of the extrusion speed, compressing the rod-like material so formed, while maintaining its substantially cylindrical form, by rolling it between two surfaces spaced apart by a distance less than the initial diameter of the rod-like material, at least one of the said surfaces being at a temperature at which the thermoplastic filamentforming material softens, and subsequently forming said material into cigarrette filter tips.

13. Process which comprises extruding a solution of a cellulose acetate into a coagulating liquid consisting of a non-solvent for the cellulose acetate in which the concentration of solvent is kept below 20% by weight through at least 400 orifices of diameter between 0.025 and 0.125 mm. distributed over substantially the whole of a circular area and spaced apart by 0.251.5 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between and 6 of the extrusion speed, compressing the rod-like material so formed, while maintaining its substantially cylindrical form, by rolling it between two surfaces spaced apart by a distance less than the initial diameter of the rod-like material, at least one of the said surfaces being at a temperature at which the cellulose acetate softens, and subsequently forming said material into cigarette filter tips.

14. Process according to claim 1, which comprises the step of compressing the rod-like material, while mainspasms taining its substantially cylindrical form, by passing it through at least one circular die of diameter less than that of the rod-like material before it enters the die.

15. Process which comprises extruding a solution of a thermoplastic filament-forming substance into a coagulating liquid through at least 400 orifices distributed over substantially the whole of a circular area and spaced apart by 0.251.5 mm. between centres, drawing the mass of filaments so formed through and out of the coagulating liquid at a take-up speed which is between /3 and 1 of the extrusion speed, compressing the rodlilte material so formed, while maintaining its substantially cylindrical form, by passing it through at least one circular die of diameter less than that of the rod-like material before it enters the die, the die being at a temperature at which the thermoplastic filament-forming material softens, and subsequently forming said material into cigarette filter tips.

16. Process according to claim 1, which comprises the steps of compressing the rod-like material, while maintaining its substantially cylindrical form, after it has left the coagulating liquid, and smoothing the surface of 3 the compressed rod-like material by subjecting it to the simultaneous action of friction and a solvent for the filament-forming substance of which the rod-like material is made.

References Cited in the file of this patent UNITED STATES PATENTS 211,009 Hagerty Dec. 17, 1878 993,308 Lamont May 23, 1911 2,036,860 Dreyfus Apr. 7, 1936 2,041,798 Taylor May 26, 1936 2,079,133 Taylor May 4, 1937 2,156,455 Kleine et a1. May 2, 1939 2,174,575 {Forrest Oct. 3, 1939 2,249,745 Charach et al. July 22, 1941 2,374,540 Hall Apr. 24, 1945 2,455,174 Hitt Nov. 30, 1948 2,465,408 Webb et a1 Mar. 29, 1949 2,553,483 Sowter et a1. May 15, 1951 2,700,794 Taylor et al. Feb. 1, 1955 2,854,985 Watkins Oct. 7, 1958 2,916,777 Crane et a1. Dec. 15, 1959 

1. PROCESS WHICH COMPRISES EXTRUDING A SOLUTION OF A FILAMENT-FORMING SUBSTANCE INTO A COAGULATING LIQUID THROUGH AT LEAST 200 ORIFICES DISTRIBUTED OVER SUBSTANTIALLY THE WHOLE OF A CIRCULAR AREA AND SPACED APART BY LESS THAN 2 MM. BETWEEN CENTRES, DRAWING THE MASS OF FILAMENTS SO FORMED THROUGH AND OUT OF THE COAGULATING LIQUID AT A TAKE-UP SPEED WHICH IS LESS THAN HALF THE EXTRUSION SPEED AND COMPRESSING SAID MASS INTO A CYLINDRICAL STRUCTURE OF PREDETERMINED CROSS-SECTION. 